This invention is in the field of electronic circuits, and is more specifically directed to switching voltage regulators.
As is well known in the electronics art, stable voltage levels are of tremendous importance in many circuit and system applications, particularly those in which the absolute voltage level impacts the accuracy or fidelity of the resulting system. One such system application in which stable voltages are essential is the well-known magnetic disk drive, in which data is written and read to magnetic media. Modern disk drives typically use a servo-controlled “spindle” motor to rotate the disk surfaces under a flying magnetic read-write head, and a servo-controlled “voice-coil” motor to move and control the radial position of the head over the magnetic disk drive surfaces. These motors, and also the read and write amplifier circuitry, require stable voltages in order for the data storage and retrieval to be accurate and reliable.
Switching regulators are well-known voltage regulator circuits that generate a stable, regulated, voltage at an output, by rapidly switching power transistors (typically metal-oxide-semiconductor field-effect transistors, or MOSFETs) on and off. These switching regulators are thus able to quickly establish and efficiently maintain a well-regulated output voltage over a wide range of load characteristics. The regulation function is accomplished by feedback control of the switching of the power MOSFET devices. For example, in the case of a push-pull power output stage, if the output voltage is below the desired level, the duty cycle of the pull-up device can be increased to pull up the voltage at the output; conversely, if the output voltage is too high, the duty cycle of the pull-down device can be increased to pull the output voltage down to the desired level. Other output configurations can also be feedback-controlled, as appropriate. Modern switching regulators are typically highly efficient, dissipate modest amounts of power, and occupy relatively small chip and circuit board area, and as such are well-suited for applications such as magnetic disk drive systems.
As will be evident to those skilled in the art, switching regulators can either have their power MOSFET output driver transistors integrated into the same integrated circuit as the feedback and control circuitry (i.e., “on-chip”), or instead can have terminals to which external power MOSFET devices are connected and driven by the regulator circuit (i.e., “off-chip”). The decision of whether on-chip power MOSFET output driver transistors are sufficient or whether instead off-chip power MOSFET output driver transistors are to be used is made by the system designer, based on such factors as the expected load to be presented to the regulator, the form factor and integrated circuit board space available for off-chip MOSFETs, heat dissipation considerations, and the like.
However, to the integrated circuit manufacturer, it is inefficient from the standpoint of design and manufacturing resources, as well as from an inventory control and forecasting standpoint, to provide switching regulator integrated circuit devices of separate types for each regulator design, one type having on-chip power MOSFET output driver transistors included in the integrated circuit, and the other type arranged for driving off-chip power MOSFET devices. This inefficiency becomes especially costly for controller and power management devices that integrate programmable and complex control functions, along with one or more switching regulators, into a single integrated circuit. These large-scale single-chip power management integrated circuits are becoming especially desirable for small form-factor systems, such as the miniaturized disk drive systems now popular in modern laptop computers, and portable audio players.
Accordingly, it would be desirable to include both on-chip power MOSFET output devices, and also the capability and interface circuitry for off-chip power MOSFET devices, in modern integrated circuits that realize switching regulators. However, especially where power dissipation is a concern (as is the case in small form-factor systems such as those mentioned above), it is undesirable to operate the switching regulator to drive on-chip power MOSFET devices when the integrated circuit is in fact being used to drive off-chip power MOSFET devices. In addition, the switching of the on-chip power MOSFET devices when off-chip power MOSFET devices are being used generates substantial noise in the system, degrading the ability of the switching regulator to maintain a stable output voltage and also generally degrading the operation of the system. It is also not possible, in some system applications, to programmably control the switching regulator to select one of its two possible outputs. The use of a jumper or other hard-wired selection technique to make this selection is cumbersome to the system implementer, and in fact may not be available in some applications.